Most household gas boilers employ a semi Bunsen burner due to stable inflammability. This semi Bunsen burner mixes some air (primary air) supplied from a blower with gas fuel in advance and supplies the mixture to a combustion unit to form a flame. The semi Bunsen burner supplies the rest of the air (secondary air) supplied from the blower to a flame forming part, thereby inducing complete combustion.
To prevent harmful emissions (e.g. CO) from being excessively discharged from such a burner, the output of the burner is generally required to be less than 2,000 kcal/h. In this case, when the output per burner unit is designed to be low, many burner units should be installed to meet the maximum output required from the boiler. As such, the overall volume of the boiler is increased.
To overcome this problem, a premix burner characterized by a small volume, high load, and low NOx has been used. However, the premix burner is difficulty to control because the range of an air ratio for stable combustion is narrow.
A high-load burner based on a concept of a lean-rich burner adopting advantages of the aforementioned burners has been developed and used. The lean-rich burner is designed so that flame parts in which excessive air is burned on one side and flame parts in which excessive gas is burned on the other side are alternately provided. In the burner having this structure, a mixed gas ejected from the two types of flame parts participates in mutual combustion, so that stable high-load combustion and low NOx combustion can be carried out by the burner having a small volume.
Most lean-rich burners are designed in the form of a dual gas pipe (in which one gas pipe is used for an air-rich mixture and the other gas pipe is used for a gas-rich mixture), and thus have a complicated structure and a large number of parts, which leads to an increase in manufacturing cost.
Meanwhile, a gas burner that alternately forms a main flame and an auxiliary flame is disclosed in Korean Utility Model Application Publication No. 1992-1735. This gas burner has the same structure as a burner in which a mixture of the same air ratio is divided into and burnt in two flame parts and one flame part is widened in a combustion area, rather than the concept of a lean-rich burner that enables stable combustion on the basis of different air ratios of the main flame and the auxiliary flame. Thus, it is impossible to expect a correlative reaction of an air-rich flame and a gas-rich flame as in the lean-rich burner.